CN111485260A

CN111485260A - Low-warpage electrolytic copper foil for secondary battery and method for producing same

Info

Publication number: CN111485260A
Application number: CN202010364561.5A
Authority: CN
Inventors: 李永根; 廖平元; 刘少华; 叶铭; 李建国; 彭颂; 李奇兰; 朱恩信
Original assignee: Guangdong Fine Yuan Science Technology Co Ltd
Current assignee: Guangdong Fine Yuan Science Technology Co Ltd
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2020-08-04
Anticipated expiration: 2040-04-30
Also published as: CN111485260B

Abstract

The invention discloses a low-warpage electrolytic copper foil for a secondary battery and a manufacturing method; belongs to the technical field of electrolytic copper foil of new energy automobile power batteries; the technical key points comprise that: the copper foil obtained after stripping from the cathode roller is called mother foil, and the electrolytic copper foil obtained by electroplating a thin copper layer on the smooth surface of the mother foil is called sub-foil; the warping amount of the child foil is below 1/4 of the warping amount of the mother foil; the surface density of the sub-foil is 1-1.02 times of that of the mother foil. By adopting the low-warpage electrolytic copper foil for the secondary battery and the manufacturing method, the warpage performance of the ultrathin copper foil can be effectively improved.

Description

Low-warpage electrolytic copper foil for secondary battery and method for producing same

Technical Field

The invention relates to the field of electrolytic copper foil for new energy automobile power batteries, in particular to a low-warpage electrolytic copper foil for secondary batteries and a manufacturing method thereof.

Background

With the rapid development of the new energy power automobile industry, high-quality electrolytic copper foil materials with good stability are becoming more and more important. At present, in the production process of electrolytic copper foil, the warping problem of the copper foil is a problem faced by many manufacturers due to factors such as the configuration of additives, the surface quality of a cathode roll, the stress of the copper foil peeling off the cathode roll, and inclusions in the surface treatment process.

For the problem of copper foil warpage, the applicant searched EPO, Himmpat, CNKI, and ten thousand databases, and the following studies were made:

first, heat treatment. Such as: CN 209459346U, CN109385648A, after the electrolytic copper foil is stripped from the cathode roller and wound to a winding roller, the winding roller is placed in a heat treatment device, and the copper foil is subjected to heat treatment to reduce the warping problem.

In the second category, the composition of the electrolyte additive is changed, and the problem of warping is solved when the foil is generated.

CN102965698A (Shandong Jinbao electronic Co., Ltd.) gives an electrolyte: cu²⁺70-80g/l，H₂SO430-40g/l, temperature of 48-50 deg.C, current density of 7000A/m²The additive collagen is low molecular weight collagen, and the molecular weight of the collagen comprises: 1000-10000 Dalton, concentration of collagen in electrolyte: 10-40 ppm.

CN104762642A (Lingbaoxinxin copper foil, LLC) shows the electrolyte composition, Cu2+ concentration 70 g/L-95 g/L, H2SO4 concentration 90 g/L0-120 g/L1, hydroxyethyl cellulose 3 g/L-30 g/L, gelatin 2 g/L-35 g/L, additive A5 g/L-35 g/L, additive B1 g/L-20 g/L, the process conditions of the electrolytic foil generation step are that the temperature is 45-55 ℃, the current density is 45-70A/m2, additive A is one or more of polyethylene glycol, sodium polydisulfane sulfonate and thiourea, and additive B is one or more of amide, HCl and saccharin sodium.

The study of the low warpage process of electrodeposited copper foil (fan and bin, scientist 2016) used CN104762642A for the production of bifocal 10 micron copper foil with warpage below 10 mm.

CN105002524A (Lingbaoxinxin copper foil, Limited liability company) discloses a foil-forming process, wherein the copper ion content in copper sulfate electrolyte is 70-120 g/L, the H2SO4 concentration is 80-110 g/L, the chloride ion content is 15-25 ppm, the temperature is 45-55 ℃, the current density during foil forming is 20-35A/m 2, and the additive in the electrolyte is SPS, polyethylene glycol, thiourea and Cl which are brightening agents^-The additive contains SPS 6-17 g/l, polyethylene glycol 2-15 g/l, thiourea 4-15 g/l, and Cl^-The concentration is 15-25 ppm; the solution in the anti-oxidation electroplating bath during the anti-oxidation treatment comprises the following components: the content of Cr6+ is 0.1-0.5 g/l, the pH value is 1.0-4.0, and the temperature is 25-40 ℃.

JP6190980A discloses a low-warpage copper foil, wherein the curling amount y of the electrolytic copper foil is less than or equal to 40/x, wherein x represents the thickness of the copper foil, the method comprises the steps of enabling the sulfuric acid concentration to be 30-40g/L and enabling the copper concentration to be 40-150 g/L, and enabling an electrolyte additive to comprise an additive (A) and an additive (B);

wherein, the additive (A): thiourea or thiourea derivatives, such as: thiourea (CH)₄N₂S), N' -dimethylthiourea (C)₃H₈N₂S), N' -diethylthiourea (C)₅H₁ ₂N₂S), tetramethyl thiourea (C)₅H₁ ₂N₂S), thiosemicarbazide (CH)₅N₃S), N-allylthiourea (C)₄H₈N₂S), ethylene thiourea (C)₃H₆N₂S) and the likeAnd thiourea derivatives. Among them, N-allylthiourea, N '-diethylthiourea and N, N' -dimethylthiourea are particularly preferable;

wherein, the additive (B): any one or combination of free polyethylene glycol, polyallylamine and polyacrylic.

CN109267111A (Hubei institute of engineering), copper ion content of 60-120 g/L, sulfuric acid content of 80-150 g/L, and chlorine ion content of 10-30 ppm;

the content of the additive A in the electrolyte is 15-50ppm, and the weight ratio of the additive A to the additive B is 30-50: 60-100 parts of;

the additive A comprises a grain refiner and a polyethyleneimine alkyl compound;

the additive B comprises collagen and carboxymethyl chitosan.

CN109763152A (Lang Bao Huaxin copper foil, Limited liability company) provides anti-warping electrolyte for 6 micron ultrathin copper foil, wherein the electrolyte comprises copper ion concentration of 70-100 g/L, H2SO4 concentration of 80-130 g/L, chloride ion concentration of 25-45ppm, copper sulfate electrolyte temperature of 45-55 ℃, additives comprise KH-5 aqueous solution with concentration of 2-6 g/L, low molecular glue solution with concentration of 4-8 g/L and poly-di-sodium-dipropylsulfonate aqueous solution with concentration of 4-8 g/L, and during electrolysis, the additives are added into the copper sulfate electrolyte according to the flow rate of KH-5 of 50-100m L/min, low molecular glue of 50-100m L/min and poly-di-sodium-disulfate of 150m L/min, and the upper liquid flow rate of the copper sulfate electrolyte is 40-60m³/h。

CN110093635A (fujian qingjing copper foil limited): the temperature of the electrolyte is controlled to be 50-60 ℃, and the current density is 38-45A/m²，Cu²⁺The concentration is 90-95 g/L, H₂SO₄The concentration is 100-110 g/L, the gelatin concentration is 100-300ppm, the concentration of ceric sulfate is 0.5-10 ppm, the concentration of MESS is 1-20 ppm, the concentration of SPS is 10-50 ppm, Cl^-The concentration is 10-30 ppm.

CN110644021A (innovative materials ltd, holy city) discloses an electrolyte: 2.5-3g/l polyquaternium-10, 3.5-4g/l polyquaternium-7, 2.5-3g/l polyquaternium-51, 2-2.5g/l sodium polydithio dipropyl sulfonate, 0.75 to 1.25g/l of sodium thiolpropanate, less than or equal to 0.5g/l of gelatin, less than or equal to 0.5g/l of basic safranine dye, less than or equal to 0.5g/l of N-butylthiourea, 0.75 to 1.25g/l of sodium mercaptoimidazole benzenesulfonate and less than or equal to 0.75g/l of polyethylene glycol formal, and the liquid inlet flow rate is 25 to 55m³And h, the raw foil current is 15000A-20000A.

Third, a rolling method.

US9287566B1 discloses an anti-warping double-light 6 micron copper foil, which is prepared by firstly producing double-light 6 micron electrolytic copper foil, and then rolling the copper foil by a rolling machine, wherein the size of a roller of the rolling machine is × 250 mm (diameter) 250 mm (width), the hardness is 62-65 HRC, and the roller material is high-carbon chromium bearing steel.

In one embodiment described therein, the copper foil is rolled through a speed of 1 meter/minute and a pressure of 5000 kg until the thickness is reduced by at least 0.3%.

In another embodiment described therein, the copper foil is rolled through a speed of 1 meter/minute and a pressure of 5000 kg until the carbonaceous layer reaches a density of 1.5 g/cc.

Meanwhile, it is explicitly stated in this document that: the copper foil with the rough surface having MD glossiness of 330-620 has better anti-warping effect by a rolling method; while for the rough surface, the gloss is less than 330MD (e.g. 198), and the warpage height is still 12mm after rolling, i.e. no particularly good warpage effect is obtained.

Fourth, the roughening-curing method

CN108677225A (shandong jinbao electronic products ltd) which shows a composition comprising: pickling, special roughening, special curing, roughening, curing, zinc-nickel alloy plating, anti-oxidation treatment, silane coupling agent treatment and drying. According to the invention, the rough surface of the copper foil is specially treated, so that the compressive stress of the rough surface is increased, the stress of two surfaces of the copper foil is further balanced, the residual stress of the copper foil is further reduced, and the reduction of the warping of the copper foil is realized.

Wherein, the special coarsening process conditions are as follows: CuSO₄·5H₂O 60～110g/L，H₂SO₄170-220 g/L, 9-15 g/L of additive, 20-50 ℃ of temperature and 20-35A/m of current density₂Time of day2～5s；

Wherein the special curing process conditions are as follows: CuSO₄·5H₂O 220～290g/L，H₂SO₄100-140 g/L, 15-30 ppm of protein powder, 2-15 ppm of hydroxyethyl cellulose, 1.6-5 ppm of sodium polydithio-dipropyl sulfonate, 45 ℃ of temperature, 15-30A/m 2 of current density and 2-5 s of time.

The processing objects and effects of the above-described methods are recorded in table 1 (in the table "-" means that the warpage amount is not tested in the document and no specific numerical value is given).

For the first method, the heat treatment method is a process (close to the common knowledge) well known to engineers in the field of copper foil production, which is relatively small in applicable objects, for example, it is generally effective in treating a copper foil of 6 to 12 μm (the amount of reduction in warpage is not significantly changed as compared with the case of not performing heat treatment), and this tendency is more significant as the copper foil is thinner (i.e., the thinner the copper foil is, the less applicable the heat treatment method is).

For the second method, the additive method has a smaller application range for the lithium electrolytic copper foil. For lithium electro-copper foils, the current trend is: reduced thickness, increased strength, increased elongation; for the latter three main parameters, it is not easy to obtain better effect by adjusting the additives; in order to obtain a better warping amount, the indexes of other copper foils are necessarily reduced. The complexity can be seen from the research on metallurgy and materials of the high-performance double-lithium-ion electro-copper foil low-warpage process.

As for the third method, the rolling method is a method having a better effect, which takes into account the practice of rolling the copper foil; the defects are mainly as follows: the efficiency is low, and continuous rolling is needed; meanwhile, due to rolling, core indexes such as thickness, strength and elongation of the copper foil can be influenced to a certain degree, and process control such as rolling speed and rolling force is complex.

For the fourth method, which targets a copper foil of 18 μm, the greater the thickness, the smaller the warpage itself. In the references: the method comprises the following steps of' electrolytic copper foil warping reason analysis, bin easy and smooth, special casting and non-ferrous alloy, and the like, wherein 18-micron copper foils of 5 copper foil factories are researched in 2015, 2 copper foils are smaller than 5m, and 2 copper foils are smaller than 10 mm; only 1 family is larger than 10 mm; that is, in the case of a copper foil having a thickness of 18 μm, the amount of warpage is not so large even without processing, and therefore, the effect of the processing for the matte surface on the warpage is to be further investigated.

TABLE 1 treatment object of various methods and its effect

For the high-strength ultrathin lithium-ion copper foil for the new-generation power battery, a double-sided light high-strength lithium-ion copper foil with the thickness of 6-8 microns is currently adopted, and the lithium-ion copper foil does not need surface treatment such as roughening and curing (the roughening and curing treatment can increase the thickness of the copper foil and can inhibit warping), so the warping amount of the lithium-ion copper foil is often large; when the coating of the negative electrode material is carried out as a negative electrode current collector, the problems cause corner fracture in an automatic coating process by customers, and certain negative effects are caused to production and application of downstream customers.

Disclosure of Invention

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to provide a low-warpage electrolytic copper foil for a secondary battery.

The present invention is directed to a method for manufacturing an electrolytic copper foil, which overcomes the above-mentioned disadvantages of the prior art.

A low-warpage electrolytic copper foil for secondary batteries, wherein a copper foil obtained after peeling from a cathode roll is called a mother foil, and a smooth surface of the mother foil is treated by electroplating a thin copper layer to obtain the electrolytic copper foil which is called a sub-foil;

the warping amount of the child foil is below 1/4 of the warping amount of the mother foil;

the surface density of the sub-foil is 1-1.02 times of that of the mother foil.

Further, a difference between Ra of the plain surface of the child foil and Ra of the plain surface of the mother foil is less than 0.1 μm, and a difference between Rz of the plain surface of the child foil and Rz of the plain surface of the mother foil is less than 0.1 μm.

Further, the thickness of the electrolytic copper foil is 6-12 μm.

Furthermore, the electrolytic copper foil is a high-strength copper foil, and the normal-temperature tensile strength of the electrolytic copper foil is greater than 400 MPa.

Further, the electrolytic copper foil is a high-elongation double-sided optical lithium electrolytic copper foil, and the elongation of the electrolytic copper foil is more than 5%; more preferably, greater than 7%.

Furthermore, the glossiness of the smooth surface of the mother foil-the glossiness of the smooth surface of the child foil is less than or equal to 150GU, and the glossiness of the smooth surface of the child foil is greater than 100GU and less than 400 GU.

Further, the glossiness of the smooth surface of the mother foil-the glossiness of the smooth surface of the daughter foil are less than or equal to 50GU, and the glossiness of the smooth surface of the daughter foil is 150 GU-200 GU.

A method for manufacturing electrolytic copper foil, after the copper foil on the cathode roller is stripped, then pass the warping processing tank;

wherein, the warpage processing groove includes: the device comprises a warping treatment tank body, a guide electrifying roller, a first anode plate, a second anode plate and a submerged roller;

the first anode plate and the second anode plate are respectively arranged on the side wall of the warping treatment tank body;

the copper foil stripped from the cathode roller enters a warping treatment tank, the smooth surface of the copper foil faces downwards, and the smooth surface of the copper foil corresponds to the first anode plate and the second anode plate;

the first anode plate and the second anode plate of the warping treatment tank are communicated with the positive pole of a power supply, and the guide electrifying roller is communicated with the negative pole;

the guiding electrifying rollers are respectively arranged on two sides of the warping processing groove body and are respectively used for guiding the direction of the copper foil into the warping processing groove and guiding the copper foil out of the warping processing groove;

the copper foil passes under the submerged roller, the rough surface of the copper foil contacts with the submerged roller, and the smooth surface of the copper foil is far away from the submerged roller.

wherein, the warpage processing groove includes: the device comprises a warping treatment tank body, a guide electrifying roller, a first anode plate, a second anode plate and a submerged roller; the first anode plate and the second anode plate are respectively and symmetrically arranged on the left side and the right side of the upper part of the submerged roller;

the copper foil stripped from the cathode roller enters a warping treatment tank, the smooth surface of the copper foil faces upwards, and the smooth surface of the copper foil corresponds to the first anode plate and the second anode plate;

the copper foil passes under the submerged roller, the smooth surface of the copper foil is in contact with the submerged roller, and the rough surface of the copper foil is far away from the submerged roller.

Further, the waste water passes through an anti-oxidation tank and a drying device after passing through the warping treatment tank.

Further, the specific process conditions of the warping treatment tank are as follows:

the composition of the copper sulfate-sulfuric acid solution in the warp treatment tank includes: cu²⁺Content 20-30 g/L, H₂SO₄The content is 100-120 g/L, and the temperature is 30-35 ℃;

the linear velocity of the copper foil passing through the warping treatment tank is 30 m/min, and the current density is as follows: 1100A/m2 for 2-3 s.

The beneficial effect of this application lies in:

firstly, the production process of the warp-resistant double-sided high-strength copper foil mainly faces the following problems in research and development:

1) the process of electroplating the surface of the copper foil is a mature process of surface treatment of the copper foil; which is generally used in the production of standard foils (i.e., printed circuit copper foils), lithium-ion copper foils for secondary batteries do not require substantial "roughening-curing" treatments because these treatments significantly increase the thickness of the copper foil (the thicker the lithium-ion copper foil is, the lower the energy storage density; while there is not much impact on the standard foil), significantly increase the internal resistance of the copper foil (the greater the roughness, the greater the internal resistance), and do not meet customer requirements. Therefore, it is proposed to treat the warpage problem of the ultra-thin dual-light high-strength lithium-ion electrolytic copper foil by electroplating a copper foil layer on the surface of the copper foil, which needs to overcome the common knowledge of engineering technicians.

2) The prior art CN108677225A is used for carrying out roughening-curing treatment on a rough surface and also gives opposite suggestions: the rough-surface electroplated layer copper foil is always researched; however, the inventor group has made many studies and has not achieved a good result in improving the warpage problem in the aspect of rough surface plating.

3) Through a plurality of discussions and researches: the copper foil is electrically settled on the smooth surface of the copper foil, so that the warping problem can be improved; however, this approach also suffers from several problems:

first, how to avoid changing the thickness of the copper foil (required for high-performance lithium-ion battery copper foil, the thickness is within ± 5%) when the thin copper foil is electrodeposited on the surface of the copper foil.

Next, how to maintain the glossiness and roughness of the surface of the copper foil when a thin copper foil is electrodeposited on the surface of the copper foil.

And then, how to maintain the strength and elongation of the copper foil when a thin copper foil is electrodeposited on the surface of the copper foil.

Second, this application compares the two processes of FIGS. 1 and 2. A surprising conclusion was reached through 4 groups of tests: the process shown in the attached drawing 2 is better than the process shown in the attached drawing 1, namely, the warped surface (rough surface) is stretched by performing a surface electroplating process on the warped back surface (smooth surface), so that the stress generated in the production process of the existing ultrathin electrolytic copper foil is effectively reduced, and the problem that the performance of the copper foil is influenced by the warping degree is solved.

It should be noted that fig. 1 and 2 illustrate a split machine to implement the present application. However, the method can also be realized by adopting a conjoined machine, namely a 'raw foil machine-warping treatment tank-anti-oxidation tank-drying device-winding roller' is a continuous and uninterrupted production line.

More excellent, the integrated machine adopts a 'raw foil machine-a slitting device-a warping treatment groove-an anti-oxidation groove-a drying device-a winding roller', and the winding roller can be directly packaged and sent to a client for use.

Thirdly, the application focuses on the relevant parameters of the smooth surface electroplating process, and finds that: current density is a key parameter; through a plurality of groups of tests, the change rules of roughness indexes of the S surface and the M surface, the change rules of surface density, the change rules of elongation and the change rules of strength under different current densities are compared.

Fourthly, the electrolytic copper foil is mainly used for a negative electrode current collector in a secondary battery, further mainly used for a negative electrode current collector in a lithium battery, and further mainly meets the high standard requirement of the lithium battery of the new energy vehicle.

Drawings

The invention will be further described in detail with reference to examples of embodiments shown in the drawings to which, however, the invention is not restricted.

FIG. 1 is a first process diagram.

FIG. 2 is a second process diagram.

FIG. 3 is a photograph of a smooth surface SEM of a 6 micron copper foil without a smooth surface plating treatment.

FIG. 4 shows a 6 μm copper foil at 1100A/m²And (5) taking a polished surface scanning electron microscope photo after treatment.

FIG. 5 shows a 6 μm copper foil at 1500A/m²And (5) taking a polished surface scanning electron microscope photo after treatment.

FIG. 6 shows a 6 micron copper foil at 2200A/m²And (5) taking a polished surface scanning electron microscope photo after treatment.

The reference numerals are explained below:

the device comprises an unwinding roller 1, a guide electrifying roller 2, a warping treatment tank 3, an anti-oxidation treatment tank 4, a drying device 5 and a winding roller 6;

a warping treatment tank body 3-1, a first anode plate 3-2, a second anode plate 3-3 and a submerged roller 3-4.

Detailed Description

The terms are explained below.

In this specification:

the S-side represents the shiny side of the copper foil, i.e., the side proximate the cathode roll.

The M-plane represents the matte side of the copper foil, i.e. the side facing away from the cathode roll.

The M-side of the present invention also has good glossiness, that is, the dual lithium ion electrolytic copper foil applied to the secondary battery of the present invention is different from the standard foil applied to the printed circuit (the M-side glossiness of the standard foil is low).

An electrolytic copper foil obtained after being stripped from a cathode roller is called a mother foil, and the electrolytic copper foil obtained by electroplating a thin copper layer on the smooth surface of the mother foil is called a sub-foil;

the surface density of the sub-foil is 1-1.02 times of that of the mother foil.

Further, the thickness of the electrolytic copper foil is 6-12 μm.

Further, the electrolytic copper foil is a high-elongation double-sided optical lithium electrolytic copper foil, and the elongation of the electrolytic copper foil is more than 5%.

Further, the present invention also relates to a method for manufacturing the copper foil,

after the copper foil on the cathode roller is stripped, winding the copper foil onto a winding roller; the copper foil electrolysis process in the process belongs to the prior art (such as CN101481810B and CN 102337566A), and does not need to be decocted in the application; for example: with the applicant's prior application: CN 102337566A, and the high-elongation double-sided light 8-micron copper foil and the high-elongation double-sided light 6-micron copper foil are produced.

The copper foil surface treatment device comprises the following components in sequence according to the advancing direction of a copper foil: the device comprises an unwinding roller 1, a guide electrifying roller 2, a warping treatment tank 3, an anti-oxidation treatment tank 4, a drying device 5 and a winding roller 6;

the warp processing bath 3 includes: a warping treatment tank body 3-1, a first anode plate 3-2, a second anode plate 3-3 and a submerged roller 3-4; the first anode plate 3-2 and the second anode plate 3-3 are respectively arranged on the side wall of the warping treatment tank body 3-1;

carrying out surface treatment on a double-sided smooth 8-micron copper foil, placing the copper foil with a rough surface upward and a smooth surface downward during unreeling of the surface treatment, enabling the copper foil to enter a warping treatment tank 3 through a guide electrifying roller 2, wherein the smooth surface of the copper foil corresponds to a first anode plate 3-2 and a second anode plate 3-3;

the first anode plate 3-2 and the second anode plate 3-3 of the warping treatment tank 3 are communicated with the positive electrode of a power supply, and the guide electrifying roller 2 is communicated with the negative electrode, and a copper sulfate solution is arranged in the warping treatment tank, so that a layer of trace copper ions can be electroplated on the polished surface, the polished surface crystal form of the copper foil tends to be more regular, the strength is improved, the stretching warping effect is achieved, and the copper foil is wound after being treated and dried by an organic anti-oxidation tank.

The dimensions of the first anode plate 3-2, and the second anode plate 3-3 are selected to be: 1400mm long, 750mm wide and 8mm thick.

Wherein the specific process conditions of the warping treatment tank are as follows:

Cu²⁺content 20-30 g/L, H₂SO₄The content of 100-120 g/L, the temperature of 30-35 ℃ and the current density of 1100A/m²And the time is 2-3 s.

The above production process mainly faces the following problems in development:

firstly, the process of electroplating the surface of the copper foil is a mature process of surface treatment of the copper foil; which is generally used in the production of standard foils (i.e., printed circuit copper foils), lithium-ion copper foils for secondary batteries do not require substantial "roughening-curing" treatments because these treatments significantly increase the thickness of the copper foil (the thicker the lithium-ion copper foil is, the lower the energy storage density; and do not have much impact on the standard foil) and are not satisfactory to customers.

Moreover, the standard foil is one of the main products of the applicant, so that a method of electroplating a copper foil layer on the surface of the copper foil to solve the warping problem is proposed for the ultra-thin dual-light high-strength lithium-ion electric copper foil, and is directly rejected in the research and development of the project.

Secondly, the prior art CN108677225A is a roughening-curing treatment for the rough surface, and the opposite suggestion is also given: the study on the rough surface electroplated layer copper foil applied to the ultrathin double-light high-strength lithium-ion electro-copper foil has been conducted, and no outstanding effect is shown on the improvement of warping.

Third, through many discussions and studies: aiming at the smooth electro-deposition copper foil of the ultrathin double-sided high-strength lithium electro-copper foil, the method faces the following problems:

firstly, when a thin copper foil is electrodeposited on the surface of the copper foil, how to avoid changing the thickness of the copper foil (the thickness is within +/-5 percent according to the requirement of the high-performance lithium battery copper foil) is avoided;

Only if the above three problems can be avoided is there a possibility to study the warpage properties.

Based on the above knowledge, several experimental studies were conducted.

First, study of a bifocal 6-micron lithium-ion electro-copper foil.

The double-light 6-micron high-strength electrolytic copper foil is obtained on a cathode roller by adopting the prior art, the double-light 6-micron high-strength lithium electrolytic copper foil is stripped on the cathode roller, then the double-light 6-micron high-strength lithium electrolytic copper foil is processed by a warping processing tank 3, and finally the double-light 6-micron high-strength lithium electrolytic copper foil passes through an anti-oxidation tank.

In order to investigate the effect under different process conditions, related tests were performed on the copper foils produced in the following 8 sets of tests.

1) Parent roll (i.e., copper foil that has not been subjected to a warp treatment bath);

2) the current density of the anode plate is 750A/m²、850A/m²、1000A/m²、1100A/m²、1200A/m²、1500A/m²、2200A/m²Copper foil in the case.

A comparison of the data from the 8 tests described above is shown in Table 2 (using the apparatus of FIG. 1).

From Table 2, it can be seen that: the current density is 1100A/m²Has good effect. It can be seen that, as the current density increases, the warpage is well controlled, that is, for the 6 micron copper foil, the smooth surface is electroplated with copper, which has a better effect on the warpage.

At the same time, the higher the current density, the higher the surface roughness of the copper foil, but the Ra and R of the surface_ZThe value is not simply linear with current density; at a current density of 1200A/m²Above, Ra and R of the smooth surface_ZThe value is remarkably increased, and the current density is 1100A/m²Ra and R of the smooth surface_ZThe value does not change much. However, the current density was 1200A/m²Above this, the roughness of the polished surface rises significantly and no longer meets the requirements of the customer.

Meanwhile, the current density is 1200A/m²The thickness of the copper foil is more than 2% of that of the mother foil.

TABLE 2 first set of tests

TABLE 3 second set of tests

The smooth surface of the copper foil is subjected to electrodeposition, and the design of the copper foil can be designed according to the attached drawings 1 and 2. Table 3 the process of fig. 2 was used, i.e. plain side up and matte side down, copper foil passed through the guiding electrifying roller 2 into the buckling treatment tank 3, passed through submerged rollers 3-4 and then left the buckling treatment tank 3.

The first anode plate 3-2 and the second anode plate 3-3 correspond to the smooth surfaces of the copper foils respectively and are arranged on two sides of the warping treatment tank body; the first anode plate 3-2 and the second anode plate 3-3 of the warping treatment tank 3 are communicated with the positive electrode of a power supply, and the guide electrifying roller 2 is communicated with the negative electrode.

As can be seen from Table 3: overall, the design of fig. 2 is better than the design of fig. 1. The influence of the current density change on the warpage is larger, and the current density is 1000-1100A/m²The method has good effect; when the current reaches 1500A/m²The roughness of the smooth surface is obviously changed, and the effect of coarsening is obvious.

As can be seen from a summary of tables 2-3, the design of fig. 2 is better compared to the design of fig. 1; at a current density of 1100A/m²The properties of the mother foil do not change much, in particular: the roughness of the smooth surface is not obviously coarsened, the characteristics of double light are still kept, and in addition, the strength, the thickness and the elongation are not obviously influenced.

Second, study of double-light 8-micron lithium-ion electro-copper foil.

The double-light 8-micron high-strength electrolytic copper foil is obtained on a cathode roller by adopting the prior art, the double-light 8-micron high-strength lithium electrolytic copper foil is stripped on the cathode roller, then the double-light 8-micron high-strength lithium electrolytic copper foil is processed by a warping processing tank 3, and finally the double-light 8-micron high-strength lithium electrolytic copper foil passes through an anti-oxidation tank.

TABLE 4 third group of tests

2) the current density of the anode plate is 750A/m²、850A/m²、1000A/m²、1100A/m²、1200A/m²、1500A/m²Copper foil in the case.

The data for the above 8 tests are compared in table 4 using the apparatus of figure 1.

From table 4, it can be seen that: at a current density of 1100-1200A/m²The method has good effect; when the current density reaches 1100A/m²Go on toThe current density is increased, and the warping amount is not greatly influenced; and similar to 6 microns, the current density reaches 1500A/m²In this case, the smooth surface is remarkably roughened.

The same 8 micron copper foil was processed using the apparatus of figure 2 and the results are shown in table 5.

From table 5, it can be seen that: at a current density of 1100-1200A/m²The method has good effect; when the current density reaches 1100A/m²In the above way, the current density is continuously increased, and the warping amount is not greatly influenced; and similar to 6 microns, the current density reaches 1500A/m²In this case, the smooth surface will be roughened to some extent.

TABLE 5 fourth set of tests

Comparing the above 4 sets of tests, it can be found that: for copper foils with different thicknesses, copper ions are electroplated on the polished surface, so that the warping amount can be effectively reduced; and, as the current density increases, the amount of warping decreases; the principle is that the stress generated in the production process of the prior ultrathin electrolytic copper foil (mainly the stress of the smooth surface) is effectively reduced by carrying out a surface electroplating process on the warped back surface (the smooth surface). However, as the current density increases, the roughness of the light surface becomes larger and larger (similar to roughening treatment), and the surface density also changes to some extent.

At the same time, the following findings are provided: the equipment process shown in figure 2 is better than that shown in figure 1. The reason is that: in the attached figure 2, the warping back surface (S surface) is electroplated, and the warping prevention effect is better from the test result because the warping surface (M surface) is stretched.

At the same time, the following findings are provided: the suitable current density ranges for different thicknesses of the mother foil are somewhat different, but overall 1100A/m²The best effect can be obtained in the vicinity.

At the same time, the following findings are provided: for the mother foils with different thicknesses, the roughness indexes Ra and Rz of the M surface of the electrolytic copper foil obtained by the process of the application are changedThe change relation between the current density and the cost is not large; the changes of the roughness indexes Ra and Rz of the S surface are as follows: the current density in the electroplating treatment is 1100A/m²In the following cases, the current density in the plating treatment was 1200A/m, although the current density was substantially unchanged²Above, both grow rapidly.

Meanwhile, in the above 4 sets of experiments, it was found that: in different tests, the brightness of the rough surface of the copper foil does not change greatly; the brightness of the smooth surface of the copper foil is closely related to the electroplating current, the relationship is also nonlinear, taking the first group of experiments as an example, the brightness of the smooth surface of the mother foil is 277GU, and the brightness of the smooth surface of the daughter foil generally tends to decrease along with the increase of the current; but at a current density of less than 1500A/m²When the above-mentioned drop value is limited (1500A/m)²When the brightness of the smooth surface of the sub-foil is 170 GU); and at a current density of more than 1500A/m²The drop value increases steeply, for example: at a current density of 2200A/m²After treatment, the brightness of the smooth surface of the sub-foil is only 50 GU. Meanwhile, the brightness of the smooth surface of the sub-foil is found to be in a nonlinear relation with the electroplating current through other three groups.

Based on the experimental findings, the electroplating current density is less than 1500A/m²As a result, the gloss of the mother foil was not more than 150GU, that of the daughter foil was 100GU to 400 GU.

In particular, at a plating current density of 1100A/m²And when the gloss of the smooth surface of the mother foil is smaller than or equal to 50GU, and the gloss of the smooth surface of the child foil is 150 GU-200 GU.

The gloss measurements were measured at 60 ° incidence.

It should be noted that:

the warpage was measured by using a disc sampler to sample a 100 × 100mm circular foil with the matte side up, placing the copper foil on a stationary platform, and measuring the warpage (i.e., measuring the maximum height of the warpage) using a steel ruler.

The measurement of the tensile strength, elongation and surface roughness of the steel sheet per unit area (corresponding to the grammage in tables 2 to 5) was conducted in accordance with DB 44/T837-2010 test.

The above-mentioned embodiments are only for convenience of description, and are not intended to limit the present invention in any way, and those skilled in the art will understand that the technical features of the present invention can be modified or changed by other equivalent embodiments without departing from the scope of the present invention.

Claims

1. A low-warpage electrolytic copper foil for secondary batteries, characterized in that a copper foil obtained after peeling from a cathode roll is called a mother foil, and the electrolytic copper foil obtained by plating a thin copper layer on the smooth surface of the mother foil is called a daughter foil;

the surface density of the sub-foil is 1-1.02 times of that of the mother foil.

2. The low-warpage electrolytic copper foil for secondary batteries according to claim 1, wherein the difference between Ra on the plain surface of the sub-foil and Ra on the plain surface of the mother foil is less than 0.1 μm, and the difference between Rz on the plain surface of the sub-foil and Rz on the plain surface of the mother foil is less than 0.1 μm.

3. The low-warpage electrolytic copper foil for secondary batteries according to claim 1, wherein the gloss of the plain surface of the mother foil-the gloss of the plain surface of the daughter foil are not more than 150GU, and the gloss of the plain surface of the daughter foil is more than 100GU and less than 400 GU.

4. The low-warpage electrolytic copper foil for secondary batteries according to claim 1, 2 or 3, wherein the electrolytic copper foil has a thickness of 6 to 12 μm.

5. The low-warpage electrolytic copper foil for secondary batteries according to claim 1, 2 or 3, wherein the electrolytic copper foil is a high-strength copper foil having a tensile strength at ordinary temperature of more than 400 MPa.

6. The low-warpage electrolytic copper foil for secondary batteries according to claim 1, 2 or 3, wherein the electrolytic copper foil is a high-elongation double-sided photo-lithium electrolytic copper foil, and the elongation thereof is more than 7%.

7. A method for manufacturing an electrolytic copper foil is characterized in that a copper foil on a cathode roll is stripped and then passes through a warping treatment tank;

8. A method for manufacturing an electrolytic copper foil is characterized in that a copper foil on a cathode roll is stripped and then passes through a warping treatment tank;

9. The electrolytic copper foil as claimed in claim 7 or 8, wherein the electrolytic copper foil is passed through an oxidation preventing tank and a drying device after passing through the warping treatment tank.

10. The electrolytic copper foil according to claim 7 or 8, wherein the specific process conditions after passing through the warping treatment tank are:

the linear velocity of the copper foil passing through the warping treatment tank is 30 m/min, and the current density is as follows: 1100A/m²And the time is 2-3 s.